The present invention relates to non-invasive methods of analyzing vibration signals from a joint by auditory display of the vibration signals. The present invention may be adapted for use with any joint in a human or animal body but is particularly useful for diagnosing disorders in a human knee joint.
Auscultation, the method of examining functions and conditions of physiological systems by listening to the sounds they produce, is one of the ancient modes of diagnosis. The first use of vibration or acoustic emission as a diagnostic aid for bone and joint disease is found in Laennec""s treatise on auscultation, cited by Mollan et al. [1]. Laennec was able to diagnose fractures by auscultating crepitus caused by the moving broken ends of bone. Heuter, in 1885, used a myodermato-osteophone, a type of stethoscope, to localize loose bodies in human knee joints. [1]. In 1929, Walters reported on auscultation of 1600 joints and detected certain sounds before symptoms become apparent [2]; he suggested that the sounds might be an early sign of arthritis.
After 1933, most of the works reported on knee-joint sounds have been on objective analysis of the sound or vibration signals, also known as vibroarthrographic (VAG) signals, for noninvasive diagnosis of knee-joint pathology [3, 4, 5, 6, 7, 8, 9 10, 11]. Although auscultation of knee joints using stethoscopes is occasionally practised by clinicians, there is no published evidence of their diagnostic value. Also, there has been no published report on computer-aided auscultation of knee-joint sounds.
Prior to graphical recording and analysis of VAG signals, auscultation of knee joints was the only noninvasive method available to distinguish normal joints from degenerative joints. Significant success has been claimed by several researchers using the auscultation technique. However, classification of knee joints by auscultation is a highly subjective technique. Further, a significant portion of the VAG signal energy lies below the threshold of auditory perception of the human ear in terms of frequency and/or intensity.
VAG signals from knee joints lie at the lower end of the frequency spectrum and the audible sound is only a part of the total vibration spectrum. The presence of background noise, muscle vibration artifacts and the complex nature of the VAG signal makes auscultation very difficult. As well, clicks of clinical interest are of short duration and direct auscultation cannot detect subtle changes or differences in such transients.
Auditory display techniques may be useful to facilitate auscultation of knee joint and other joints. Auditory display may be defined as an aural representation of a stream of data.
Therefore, there is a need in the art for methods for computer-aided auscultation of joint sounds based on auditory display (AD) techniques.